Transvenous endocardial leads may be placed inside a chamber of a patient's heart by passing the lead through a venous entry site, such as the subclavian vein or the cephalic vein, or a tributary thereof, along a venous pathway into the superior vena cava and into the right cardiac chambers. Cardiac vein leads may be advanced further, from the right atrium through the coronary sinus ostium into the coronary sinus and ultimately into one of the various cardiac veins for stimulation and/or sensing of the left heart chambers.
Cardiac lead placement is important in achieving accurate sensing of cardiac signals and proper cardiac stimulation pulse delivery for providing optimal therapeutic benefit from cardiac stimulation therapies such as cardiac resynchronization therapy (CRT). Cardiac vein leads generally need to be small in diameter to allow advancement through the cardiac veins and highly flexible in order to withstand flexing motion caused by the beating heart without fracturing. The small diameter and flexibility of the lead, however, makes advancement of the lead along a tortuous venous pathway challenging. Cardiac vein leads are generally implanted with the aid of a relatively stiff guide catheter and/or guidewire or stylet. Considerable skill and time are required to achieve proper placement of a transvenous lead along a cardiac vein site.
Cardiac vein leads have typically been provided with a passive fixation member and an atraumatic tip electrode. The passive fixation member provides fixation of the distal lead tip by becoming lodged within a narrow cardiac vein. The distal lead tip needs to be advanced into a cardiac vein that is small enough to securely lodge the lead tip therein. Dislodgement of a passively fixed cardiac vein lead can still occur, however, even when the lead tip is advanced into a small vein.
The requirement of advancing the lead into a narrow cardiac vein branch for fixation purposes imposes limitations on the possible implant locations that may be selected. An implant site in a larger vein may result in more optimal sensing or stimulation in a particular individual. Furthermore, advancement of leads deep into a small cardiac vein on the lateral free wall of the left ventricle can introduce undesired stimulation of the diaphragm during cardiac pacing.